SER Optimization in OFDM-IM Systems with Nonlinear Power Amplifiers

Abstract

Power amplifiers (PAs) lead to nonlinear distortion in index modulation assisted OFDM (OFDM-IM) systems when the peak-to-average power ratio (PAPR) is high. But PAPR reduction in OFDM-IM is more complicated than that in traditional OFDM owing to the frequent switch of subcarrier states between active and idle. When implementing OFDM-IM on resource-limited platforms like battery-powered Internet of Things (IoT) devices, PAPR cannot always be ideally eliminated due to the complexity of the reduction algorithm and the limitation of computation resources. Hence, performance optimization under non-negligible PAPR becomes an important issue. This paper performs symbol error rate (SER) optimization in OFDM-IM systems with high PAPR. First, we derive a low complexity expression of receiver signal-to-noise ratio (SNR) in nonlinear OFDM-IM systems. Second, we find that SER in OFDM-IM is affected by the nonlinear distortion in both constellation mapping and index estimation. With this observation, we derive a closed-form expression of SER and prove that there is a lower bound. Third, we do SER optimization and identify the optimal system operating point with respect to the minimum SER. Finally, we validate our analysis through simulations.